1. Field of the Invention
The present invention relates to a transparent glass antenna for an automobile. More particularly, it relates to such antenna using a transparent conductive film as an antenna conductor.
2. Discussion of Background
As a glass antenna for an automobile formed by arranging an antenna conductor in or on a glass panel which constitutes a window glass in the automobile, there have been known one which is formed by printing a conductive paste such as a silver paste in a predetermined pattern followed by baking it; one formed by arranging a fine metallic line having electric conductivity in a predetermined linear pattern; or one constituted by a transparent conductive film covering on the glass panel in a film form.
Of these glass antennas, the glass antenna having the transparent conductive film as an antenna conductor is considered to be preferred for the reason that it does not obstruct the visual field of a driver and it does not disturb the driver unlike a conventional linear antenna conductor. However, it is not always easy to obtain a sufficient sensitivity by the film-shaped antenna conductor. Therefore, trial and error has been repeated to develop a film glass antenna with an excellent pattern in gain.
The inventors of the present application have developed a transparent glass antenna having a conductor pattern providing a relatively excellent gain as shown in FIG. 10. In FIG. 10, a transparent conductive film 23 divided into three regions by slits 22 is arranged at the upper side of a glass panel 21 in which a bus bar 25 is disposed at the upper edge of the central portion of the transparent conductive film 23. A reference numeral 26 designates an antenna feeder line.
Further effort to attempt improvement in the performance of such film antenna conductor as the transparent conductive film has revealed that it is more efficient to arrange the bus bar 25 so as to surround the peripheral portion of the transparent conductive film 23 rather than that the bus bar 25 is arranged at only one side edge of the transparent conductive film 23. However, when the bus bar 25 is arranged at the edge portion of the transparent conductive film 23 partially covering the glass panel 21, the arrangement of the bus bar 25 may constitute an obstacle to the visual field of the driver, and it is undesirable as a glass antenna for an automobile.
Further, formation of the slits 22 to divide the transparent conductive film 23 into a plurality of sections on the glass panel 21 is troublesome because it is difficult to form the slits 22 with a predetermined width according to a designed value. In addition, the position for connecting the antenna feeder line 26 is restricted to be at the upper side portion of the glass panel 21 as shown in FIG. 10, for instance, in view of the arrangement of the bus bar 25. Thus, there has been many restrictions in the arrangement of the bus bar 25 and the antenna feeder line 26. The presence of the slits may disturb a driver and a passenger even though the transparent conductive film 23 is transparent.